Leela and the Doctor arrive in the scoop of a massive sandminer, Storm Mine 4, which is combing an alien world for precious ores (lucanol and zelanite amongst others) for the controlling company.
The miner is run by Commander Uvanov and his small human crew aided by numerous robots which are split into three classes: in overall control is a single Super Voc, under him come the Voc class robots, and at the bottom of the hierarchy are the mute Dum robots. Almost as soon as the Doctor and Leela escape from the scoop and into the main part of the ship, just prior to a sandstorm, mysterious deaths start to occur, beginning with the strangulation of mineralogist Chub.